/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.example.factorial;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.math.BigInteger;

/**
 * Handler for a server-side channel.  This handler maintains stateful
 * information which is specific to a certain channel using member variables.
 * Therefore, an instance of this handler can cover only one channel.  You have
 * to create a new handler instance whenever you create a new channel and insert
 * this handler  to avoid a race condition.
 *
 *
 * 服务端处理器
 *
 * 这个处理器, 维护的是一个有状态的信息 , 使用一个变量(在encode中说明) ,来确定的使用一个channel
 * 那么 , 当前处理器,只能处理这个特定的channel
 *
 * 重点:  ↓
 * 那么 , 当创建一个新的channel,并且想把当前handler放入channel时,
 * 必填创建一个新的实例来避免条件竞争
 *
 * 为什么会存在条件竞争 :
 * 当前实例对象中 ,保存了当前操作的数据
 * 如果其他的channel中也使用了这个实例对象
 *
 * 那么这个数据(接收的数据,next加的数据)将会产生并发.数据就不准确了

 *
 *
 */
public class FactorialServerHandler extends SimpleChannelInboundHandler<BigInteger> {

    /**
     * 初始阶乘基数 1  , 及记录本次数字
     */
    private BigInteger lastMultiplier = new BigInteger("1");
    /**
     *  阶乘结果记录
     */
    private BigInteger factorial = new BigInteger("1");

    @Override
    public void channelRead0(ChannelHandlerContext ctx, BigInteger msg) throws Exception {
        System.out.println(msg);
        // Calculate the cumulative factorial and send it to the client.
        // 记录本次数字
        lastMultiplier = msg;
        System.out.println("before: "+factorial);
        // 计算阶乘 . 并记录保存
        factorial = factorial.multiply(msg);
        System.out.println("after: "+factorial);
        // 这本次计算结果,发送给客户端
        ctx.writeAndFlush(factorial);
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        // 当客户端 断开链接时 , 打印出本次计算的结果,及计算的数字
        System.err.printf("Factorial of %d is: %d%n", lastMultiplier, factorial);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}
